This invention relates to adhesive compositions with reduced adhesion to skin. More particularly, it relates to adhesive compositions containing alkyl cyanoacrylates and having reduced adhesion to skin.
It has been known for many years that 2-cyanoacrylate esters make very powerful adhesives; see, for example, U.S. Pat. No. 2,794,788 issued June 4, 1957 to Coover and Shearer. Such cyanoacrylate ester adhesive compositions have become widely used because they form very powerful bonds between a wide variety of substrates; for example, cyanoacrylate ester adhesive compositions will rapidly form very strong bonds between glass, metals, plastics, wood, textiles and paper. A general review of conventional 2-cyanoacrylate ester adhesives may be found in I. Skeist (ed.), Handbook of Adhesives, 2nd Edn., Van Nostrand Reinhold Co. (1977), Chapter 34, pages 569-80. Unfortunately, such cyanoacrylate ester adhesive compositions suffer from the serious disadvantage that they also form very powerful bonds with human skin, and thus if the user of such an adhesive composition inadvertently gets even a very small amount of the adhesive composition on his finger tips or other exposed areas of skin while he is using the composition, the adhesive composition will rapidly bond the skin with which it comes into contact to another portion of the user's skin, the substrate being glued or to any other article with which the adhesive-covered skin comes into contact. Such accidental bonding of skin takes place very rapidly (within a few seconds) and the bonds thus formed are considerably stronger than human skin itself, so that if an attempt is made to tear the skin away from the object to which it has accidentally become adhered, serious damage to the skin and underlying tissue may result. Indeed, the bonds formed by cyanoacrylate esters with body tissues are to strong that such adhesive compositions have been recommended for medical and surgical use as an alternative to conventional surgical sutures for closing incisions and wounds and for repairing breaks or ruptures in bone and other tissues; see, for example, U.S. Pat. Nos. 3,223,083, issued Dec. 14, 1965 to Cobey, 3,667,472, issued June 6, 1972 to Halpern, and 3,940,362, issued Feb. 24, 1976 to Overhults. Moreover, if the cyanoacrylate adhesive composition is allowed to bond for more than a few minutes, it cures to such a degree that it is almost insoluble in all common solvents; thus by the time a person who has accidentally adhered his skin to itself or to some other material has had time to reach a first aid station or hospital emergency room, the adhesive composition has cured to a point at which the bond cannot be broken quickly or readily with any common solvents, and the breaking of such bonds is a complicated task even for skilled medical personnel. Hospital emergency room personnel frequently come into contact with such problems caused by the use of cyanoacrylate ester adhesive compositions. Methyl cyanoacrylate ester adhesive compositions produce skin bonds which are almost totally insoluble in all common solvents and are extremely difficult to break; the dangers thus associated with methyl cyanoacrylate compositions appear to have been at least a substantial factor in the withdrawal of most, if not all, methyl cyanoacrylate compositions formerly sold for household use.
The possibility of accidental skin adhesions does reduce the use of cyanoacrylate esters, since people requiring adhesive compositions may prefer to use an adhesive composition which, although forming a less powerful bond than a cyanoacrylate ester composition, does not carry the risk of accidental skin adhesions. In an industrial environment, the safety precautions necessary to prevent accidental skin adhesions may slow up the work of applying cyanoacrylate ester adhesive compositions to substrates, and thus reduce productivity. In domestic use, not only does the possibility of accidental skin adhesions make the use of cyanoacrylate ester adhesive compositions awkward in many instances, but it may reasonably be supposed that some domestic users will not buy such adhesive compositions at all, prefering the use of less powerful, and possibly more expensive, adhesive compositions rather than risk accidental skin adhesions. The risk of such accidental skin adhesions is exacerbated by the fact that most commercially-available cyanoacrylate ester adhesive compositions are, in their uncured state as applied to substrates, relatively mobile liquids which easily run from the substrate onto the fingers of a person holding the substrate.
Until now, it has been believed that the possibility of accidental skin adhesions is an inevitable concomitant to the use of cyanoacrylate ester adhesive compositions. It is believed that the curing of such compositions proceeds through an anionic mechanism, the composition being so easily polymerized that water alone is a sufficiently active compound to initiate such anionic polymerization. Indeed, it is believed that in normal use the curing of such compositions is initiated by atmospheric moisture and/or the minute amounts of water adsorbed onto most substrates. In view of the large proportion of water present in the human epidermis, it would appear inevitable that the polymerization of cyanoacrylate ester adhesive compositions would be greatly accelerated by contact with the human epidermis, and thus that all cyanoacrylate ester adhesive compositions would suffer from problems of skin adhesion.
Thus, although the problems of accidental skin adhesion associated with the use of cyanoacrylate ester adhesive compositions are well known and serious, and although these problems have reduced the desirability and volume of such adhesive compositions sold, no prior art cyanoacrylate ester adhesive composition is known which significantly reduces such problems, and hereto there have been good grounds for supposing that it was not possible to significantly reduce the skin adhesion of such compositions.